This application is related to Japanese Patent Application No. 2001-159189 filed on May 28, 2001, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a process of manufacturing a semiconductor device. More particularly, it relates to a process of manufacturing a semiconductor device in which wiring is formed on a surface of a semiconductor substrate by electrolytic plating.
2. Description of Related Art
Low resistance metals such as precious metals (e.g., Au) are commonly used as wiring materials used for semiconductor devices such as high frequency transistors and ICs. Use of such low resistance metals reduces loss of propagation of a high frequency wave. When an expensive precious metal is used, preferably the wiring is formed by a plating method rather than by a metal lift-off method since, e.g., the former uses the material more efficiently and is advantageous in increasing the thickness of the wiring. The metal lift-off method, on the other hand, causes a large waste of the material.
FIGS. 2(a) to 2(d) are sectional views illustrating the steps of manufacturing the wiring by a conventional plating method.
First, as seen in FIG. 2(a), scribe lines 24a for separating semiconductor element regions 24b are formed as described below. In a semiconductor substrate 21 on which the wiring will be formed, a semiconductor element such as a transistor has been incorporated (not shown). On the semiconductor substrate 21, an insulating film 22 is formed. The insulating film 22 can easily be processed into a mask used for etching the substrate or forming electrodes during the manufacture of the semiconductor device. Further, another insulating film 23, which is denser in film quality than the insulating film 22, is layered on the insulating film 22 to cover the entire semiconductor element for the purpose of enhancing reliability of the semiconductor element, e.g., resistance to moisture. The scribe lines 24a are formed by removing the insulating films 22 and 23 by etching or the like.
Then, a power-feeding thin metal film 25, which will be a common electrode for electrolytic plating, is formed over the insulating films 22 and 23, as well as the exposed semiconductor substrate (see FIG. 2(b)).
Next, a photoresist film 26 having openings only in regions for forming the wiring is formed on the power-feeding thin metal film 25. Then, the electrolytic plating is carried out by using the photoresist film 26 as a mask, thereby forming plated wiring 27 only in the openings in which the power-feeding thin metal film 25 is exposed (see FIG. 2(c)).
Thereafter, the photoresist film 26 is removed. Then, the power-feeding thin metal film 25 which unnecessarily remains in a region not below the plated wiring 27 is etched away by using the plated wiring 27 as a mask (see FIG. 2(d)).
Through the thus described steps, the plated wiring is formed only in a required region on the semiconductor substrate.
However, the above-described steps of forming the wiring sometimes cause the following disadvantage. More specifically, a concave portion existing on the semiconductor substrate, i.e., the scribe line 24a for separating the semiconductor elements, is formed by the etching of the insulating films 22 and 23. Among the insulating films 22 and 23, the easily processable insulating film 22 which is located below the insulating film 23 is etched at an etching rate higher than that of the upper insulating film 23 provided for enhancing the reliability such as resistance to moisture. Therefore, the side wall of the concave portion will be in an inverse tapered shape in which an edge on an upper side is protruded inward as compared with an edge on a bottom side. This is disadvantageous because the power-feeding thin metal film for electrolytic plating tends to be torn at the concave portion.
In the above-described case, the tearing of the power-feeding thin metal film can be inhibited by reducing the depth of the concave portion or increasing the thickness of the power-feeding thin metal film. However, the depth of the concave of the scribe line is determined by the thicknesses of the insulating films required in the course of the manufacture of the semiconductor device. Therefore, in order to reduce the depth, the manufacture process itself needs to be altered, which is not easy.
On the other hand, the increase of the thickness of the power-feeding thin metal film results in an increase of working time and an amount of the material to be used, which leads to an increase of the cost. Even if the depth of the scribe line is reduced or the thickness of the power-feeding thin metal film is increased, the shape of the power-feeding thin metal film at the concave portion is still unstable and fraught with possibility of the tearing. If the electrolytic plating is carried out with respect to the semiconductor element in which the power-feeding thin metal film has been torn at the concave portion, electric current is not supplied to a region where the plated wiring shall be formed, and thus the plated wiring cannot be formed. Further, the electric current which should be supplied to the above-described element is supplied to a semiconductor element in which the tearing of the film has not occurred, which may produce the plated wiring having a thickness greater than a predetermined thickness.
This implies not only the fact that an element in which the tearing of the film has occurred (and thus the plated wiring has not been formed) becomes a failed element, but also a possibility that the failed element impairs an element in which the tearing of the film has not occurred.
In view of the above-mentioned circumstances, the present invention provides a process capable of preventing the power-feeding thin metal film for electrolytic plating from tearing at the concave portion, and instead forming the plated wiring on the semiconductor substrate with stability.
Thus, according to the present invention, provided is a process of manufacturing a semiconductor device comprising the steps of: filling a photoresist in a concave portion provided on a surface of a semiconductor substrate; forming a power-feeding thin metal film for electrolytic plating on the semiconductor substrate including a surface of the thus filled photoresist; and forming wiring on the power-feeding thin metal film in a region not above the concave portion by electrolytic plating.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.